Hydrostatic transmissions have recently found considerable commercial acceptance as both vehicular transmissions and industrial transmissions. One form of a hydrostatic transmission includes a centrally located valve plate having inlet and outlet ports therein with a rotatable pump cylinder block slidably engaging one side of the valve plate and a motor cylinder block engaging the other side of the valve plate. Cam assemblies are provided for reciprocating pistons in cylinders in each of the cylinder blocks thereby delivering fluid under pressure to the motor cylinder block. The motor block rotates under the influence of fluid pressure being delivered thereto with the pistons in the motor block sliding down the motor cam assembly. The motor cylinder block is drivingly connected to an output shaft for the purpose of driving a load.
One or both of the units may be of the variable displacement type to provide an infinitely variable transmission ratio between input shaft speed and output shaft speed.
One of the disadvantages in prior hydrostatic transmission constructions, is that the cam assemblies have been difficult to machine because of their configuration or location, which may be directly within the hydrostatic transmission housing. Moreover, it is not always desirable to construct the cam support of a material suitable for slidably engaging the bearings or slippers on the ends of the pistons. That is, it may be desirable to construct the basic supporting cam member of a material such as aluminum which does not have the required hardness or strength to provide a direct bearing surface for the piston bearing slippers.
While there have in the past been provided various types of rings mounted on the basic supporting cam surface, these rings have been rigid and undeformable so that when mounted on a rigid cam member tend to rock or pivot about the high spots on the cam surface if there are significant surface irregularities. Therefore, these prior constructions have required the accurate machining of the surface upon which the thrust or bearing ring is mounted, thereby increasing the cost of the cam assembly.
It is a primary object of the present invention to reduce the problems noted above in prior art hydrostatic transmissions by providing a cam assembly which is less expensive to construct while at the same time providing the material qualities and surface finish required for excellent dynamic operation of the piston slippers.